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Before they were Native Americans, were they Beringians?

When -- and how -- did the ancestors of Native Americans become genetically distinct from Asians who crossed the Bering land bridge into Alaska and the rest of North America?

For one thing, that Bering-crossing population would have had to remain isolated from other Asian populations for many millenniums, scientists say. Now, a research team led by Dennis O'Rourke of the University of Utah is theorizing that the land of Beringia, now largely submerged beneath northern seas, had the climate and plant resources to sustain wildlife and feed a human population for thousands of years.

The Bering land bridge measured as much as 1,000 miles from north to south and as much as 3,000 miles from west to east. Scientists once thought this vast tract consisted mostly of tundra steppe, a treeless environment incapable of supporting a large human population.

But in recent years paleoecologists—scientists who study ancient environments—have been drilling sediment cores in the Bering Sea and in bogs in Alaska. The samples have yielded plant and insect fossils, as well as pollen, indicating that Beringia's tundra steppe was dotted with oases of brushy shrubs and even trees such as spruce, birch, willow, and alder.

These woody refuges could have provided fuel for fires, raw material for shelters, and cover for animals such as hares, birds, elk, and moose—game that humans could have hunted for food.

O'Rourke hopes further archaeological research in Beringia -- both on land and, with technological advances, beneath the ocean -- will provide hard evidence further backing his theory.